JP2019010378A - X-ray tomosynthesis device - Google Patents

Abstract

To provide an X-ray tomosynthesis device capable of extracting an area of a high absorber accurately without increasing a man hour excessively.SOLUTION: An X-ray tomosynthesis device extracts an area of a high absorber contained in a measurement projection data for each of a plurality of projection angles, subjects the measurement projection data of the area to conversion processing, and thereafter generates a tomosynthesis image. A high absorber processing section extracts each area for the measurement projection data at each projection angle by using a start point established on the measurement projection data at each projection angle. At this time, based on a start point established on the measurement projection data at a certain projection angle, a start point is established on the measurement projection data of the other projection angle, and thereby a start point need not be established by an operator at each projection angle.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an X-ray tomosynthesis apparatus, and more particularly to a signal processing and reconstruction technique for reducing artifact components generated from a high-absorber of a tomosynthesis image.

  The X-ray tomosynthesis apparatus is an apparatus that obtains an X-ray absorption coefficient distribution image by calculating an X-ray absorption coefficient at each point in the object from measurement projection data obtained by imaging the object from multiple directions. Usually, the X-ray absorption coefficient is used for diagnosis by replacing it with a Hounsfield Unit value normalized with air and water (-1000 for air and 0 for water).

  The X-ray tomosynthesis apparatus can generate a tomographic plane of a subject on a plurality of planes parallel to a coronal plane (Coronal plane) including a body axis direction and a left-right direction of the body. In medical practice, the use of tomosynthesis images is clinically useful because it can immediately diagnose a patient's medical condition based on tomographic planes at different positions. However, since the X-ray tomosynthesis apparatus has a small projection angle range of 20 degrees to 40 degrees, the X-ray absorption coefficient of a metal or the like is smaller than that of an X-ray CT apparatus that captures a projection angle range of at least 180 degrees. There is a problem that an afterimage is generated on an adjacent surface to a tomographic surface where a subject is located and a large superabsorber boundary portion. These are referred to herein as “superabsorber artifacts”. Superabsorbent artifacts cause a reduction in clinical diagnostic ability.

  The reason for the occurrence of the superabsorbent artifact will be described in detail. The X-ray tomosynthesis apparatus uses an analytical reconstruction method based on a filtered back projection (hereinafter referred to as FBP) method such as a well-known Feldkamp method in order to acquire a tomosynthesis image. In this FBP method, for example, a subject that causes a steep rise or fall of measurement projection data at the boundary with surrounding tissue, such as a microsphere made of a substance having a large X-ray absorption coefficient, has a shape and a shape during backprojection calculation. In order to be able to restore the absorption value, a high-frequency emphasis reconstruction filter is applied to the measured projection data. The reconstruction filter is designed so that the high-frequency information is canceled on the reconstructed image when the back projection operation is performed on the measurement projection data collected in the imaging angle range of at least 180 degrees. Therefore, when the imaging angle range is small as in the X-ray tomosynthesis apparatus, the shape and absorption value of the subject in which the difference in the measured projection data value from the surrounding tissue is steep like the high absorber cannot be completely restored. Artifacts occur due to the high-frequency components emphasized by the law.

  In order to reduce this artifact, a method has been proposed in which the absorption value of the surrounding tissue is used to replace the value of the superabsorbent region to reduce the difference from the surrounding tissue, and a method of separating the high absorption material from the measured projection data. Yes.

  Patent Document 1 discloses a technique for extracting a high-absorber region of radiation from projection data acquired by tomosynthesis imaging, and calculating a feature quantity of the size and / or shape of the extracted high-absorber region. . This technique determines an interpolation method for interpolating pixels of the high-absorber region in the projection data based on the calculated feature amount. Using the determined interpolation method, the superabsorber region of the projection data is interpolated. The use of binarization processing or graph cut processing is disclosed as a method for extracting a superabsorbent region.

JP 2016-112248 A

  The technique of Patent Document 1 calculates the feature quantity of the extracted superabsorber region size and / or shape, and determines an interpolation method for interpolating pixels of the superabsorber region in the projection data. For this reason, it is important to accurately extract the superabsorbent region in order to obtain an image with reduced artifacts.

  For a medical image such as a tomosynthesis image with a large change in pixel value in one image, it may be difficult to extract a region by threshold processing such as binarization processing. Therefore, in order to accurately extract the superabsorbent region, the region is extracted by expanding (or reducing) the region based on the point or region where the region extraction is started, as in the known region expansion method. It is conceivable to use a method to do this. For example, the region expansion method is a method in which, when the pixel value of a pixel near the start point satisfies a predetermined condition, the region is sequentially expanded by adding to the region. For this reason, in order to use these region extraction methods, it is necessary to set a point or region for starting region extraction. There are at least 20 or more measurement projection data for each projection angle acquired by tomosynthesis imaging, and it is necessary to set a start point and a start area for each measurement projection data in order to perform the area expansion method or the like. And the increase in man-hours required for setting the start area becomes a problem. When the operator sets the start point and the start area, the load is on the operator.

  An object of the present invention is to provide an X-ray tomosynthesis apparatus that can extract a region of a superabsorbent with high accuracy without excessively increasing the number of steps.

  In order to achieve the above object, an X-ray tomosynthesis apparatus according to the present invention includes an X-ray generation unit that irradiates a subject with X-rays, and an X-ray that obtains two-dimensional measurement projection data by detecting X-rays that have passed through the subject. An imaging unit having a mechanism unit that moves at least one of the detection unit, the X-ray generation unit, and the X-ray detection unit relative to the subject and irradiates the subject with X-rays from a plurality of different projection angles, and a plurality of the projections The X-ray high-absorber region included in the measurement projection data for each angle is extracted, and the high-absorber processing unit that converts the measurement projection data value of the region and the high-absorber processing unit processed An image reconstruction unit that reconstructs a tomosynthesis image based on a plurality of the later measured projection data. The high-absorber processing unit extracts a region for each of the measurement projection data for each projection angle by using the start points set on the measurement projection data for each projection angle. Based on the start point set in the measurement projection data at one projection angle, the superabsorbent body processing unit sets the start point in the measurement projection data at another projection angle.

  ADVANTAGE OF THE INVENTION According to this invention, the X-ray tomosynthesis apparatus which can extract the area | region of a high absorber accurately can be provided, without making a man-hour increase excessively.

FIG. 3 is a block diagram illustrating a hardware configuration of each unit of the X-ray tomosynthesis apparatus according to the first embodiment. 1 is a functional block diagram of an X-ray tomosynthesis apparatus in Embodiment 1. FIG. FIG. 6 is a diagram for explaining a shooting condition reception screen in the first embodiment. In Example 1, (a) a functional block diagram illustrating the function of the superabsorbent body processing unit, (b) an explanatory diagram illustrating a processing result of the three-dimensional differentiation processing unit, and (c) a processing result of the three-dimensional region expansion unit 163 (D) Explanatory drawing which shows the processing result of the two-dimensional differentiation process part 164, and the starting point 43, (e) Explanatory drawing which shows the processing result of a two-dimensional area expansion part. It is a flowchart figure for demonstrating the calculation procedure of the superabsorbent body process part in Example 1. FIG. 6 is a diagram for explaining projection data and a tomosynthesis image processed by the X-ray tomosynthesis apparatus in Embodiment 1. FIG. FIG. 7 is a diagram for explaining processed projection data and tomosynthesis images different from those in FIG. 6 in the first embodiment. FIG. 8 is a diagram for explaining projection data and a tomosynthesis image obtained by performing processing different from those in FIGS. 6 and 7 in the first embodiment. It is a figure for demonstrating the phantom simulation which simulated the high absorber in the inside of spherical water in Example 1. FIG. FIG. 6 is a diagram for explaining a result of creating measurement projection data from a phantom in Example 1. It is a figure for demonstrating the result of the FBP method with or without metal artifact correction in Example 1. It is a functional block diagram explaining the function of the superabsorbent body processing part in Example 2. (A) And (b) It is a figure for implementing the interpolation process in Example 2, and explaining measurement projection data creation with connection. It is a functional block diagram explaining the function of the superabsorbent body process part in Example 3. (A) And (b) It is a figure for demonstrating performing the pattern recognition process in Example 3, and producing the measurement projection data with connection. It is a functional block diagram explaining the function of the superabsorbent body process part in Example 4. (A) is a figure for demonstrating optimization of the parameter for substance search in Example 4, (b) to (d) demonstrates the example whose extraction result of the absorber in Example 4 is inappropriate. It is a figure for doing. It is a functional block diagram explaining the function of the superabsorbent body process part in Example 5. (A) And (b) is a figure for demonstrating the measurement projection data before and behind Log conversion in Example 5. FIG. FIG. 20 is a functional block diagram illustrating functions of an image reconstruction unit in the seventh embodiment. FIG. 20 is a flowchart for explaining a calculation procedure of an image reconstruction unit in the seventh embodiment.

  Hereinafter, various embodiments of the present invention will be sequentially described with reference to the drawings.

  FIG. 1 is a diagram illustrating a hardware configuration of an X-ray tomosynthesis apparatus according to the first embodiment, and FIG. 2 is a functional block diagram illustrating functions of the X-ray tomosynthesis apparatus according to the first embodiment. As shown in FIG. 2, this embodiment includes at least an imaging unit 102, a high-absorber processing unit 136, and an image reconstruction unit 137. As shown in FIG. 1, the imaging unit 102 includes an X-ray generation unit 1 that irradiates the subject 3 with X-rays, and an X-ray detection unit that detects X-rays transmitted through the subject 3 and obtains two-dimensional measurement projection data. 2. A mechanism unit that moves at least one of the X-ray generation unit and the X-ray detection unit relative to the subject 3 and irradiates the subject 3 with X-rays from a plurality of different projection angles. The superabsorber processing unit 136 extracts X-ray superabsorber regions included in the measurement projection data for each of a plurality of projection angles, and converts the measurement projection data values of the regions. The image reconstruction unit 137 reconstructs a tomosynthesis image based on a plurality of measurement projection data processed by the superabsorbent body processing unit 136.

  Here, the high-absorber processing unit 136 uses the start points set on the measurement projection data 405 for each projection angle (see FIG. 6 described later), and the high-absorption for the measurement projection data 405 for each projection angle. The body region 404 is extracted.

  Based on the start point set in the measurement projection data 405 at one projection angle, the superabsorbent body processing unit 136 sets the start point for the measurement projection data at another projection angle.

  As described above, in the present embodiment, the superabsorbent body processing unit 136 sets the start point for the measurement projection data of other projection angles based on the start point set in the measurement projection data 405 of one projection angle. In order to set, the operator only needs to set one start point, and the region of the superabsorbent can be extracted based on the start point without increasing the man-hours of the operator.

  The start point here refers to a point where region extraction starts or a point included in a region (shape) where region extraction starts. The superabsorber processing unit 136 extracts the superabsorber region by using a method of extracting the region by expanding (or reducing) the start point or the region (shape) including the start point.

  For example, the superabsorbent body processing unit 136 has a more detailed configuration shown in FIG. 4A described later, but includes a three-dimensional material search unit 151. As shown in FIG. 4B, the three-dimensional material search unit 151 has a three-dimensional (x, y, z) in which two-dimensional (x, y) measurement projection data are arranged in the projection angle direction (θ = z). The three-dimensional derivative of the measured projection data is partially differentiated with respect to the x, y, and z coordinate axes. Then, the three-dimensional substance search unit 151 determines, based on the differential value, whether adjacent data satisfies a predetermined condition with respect to the start point 41 set in advance in the measurement projection data of one projection angle. When the differential value satisfies a predetermined condition, the three-dimensional material search unit 151 sequentially expands the high absorber region in the direction of the adjacent data from the start point 41. The three-dimensional substance search unit 151 extracts a three-dimensional superabsorbent region by performing this process in the three-dimensional direction (region expansion method, see FIG. 4C). The three-dimensional material search unit 151 determines one or more points in the range (see FIG. 4D) that the extracted three-dimensional superabsorbent region occupies in the two-dimensional measurement projection data at other projection angles. The projection angle is set as the starting point in the two-dimensional measurement projection data.

  Moreover, the superabsorbent body processing unit 136 may further include a two-dimensional substance search unit 152 shown in FIGS. 4D and 4E described later. The two-dimensional material search unit 152 calculates a two-dimensional derivative of the two-dimensional measurement projection data by partial differentiation with respect to the x and y coordinate axes (FIG. 4D). The two-dimensional substance search unit 152 determines whether adjacent data satisfies a predetermined condition with respect to the start point set by the three-dimensional substance search unit based on a two-dimensional differential value, and the differential value satisfies the predetermined condition In this case, the superabsorber region is extracted by expanding the superabsorber region in the direction of the adjacent data from the start point (region expansion method, FIG. 4 (e)).

  The superabsorbent body processing unit 136 includes an extraction region conversion unit 153. The extraction region conversion unit 153 converts the measurement projection data value of the high absorber region 404 into the measurement projection data value when the X-ray absorption rate is lower than that of the high absorber without using the values of the peripheral region (FIG. 6).

  Then, the image reconstruction unit 137 performs image reconstruction using the measurement projection data after the conversion process, so that even if the FBP method is used, the measurement projection data value when the X-ray absorption rate is low is obtained. Since the conversion process is performed, it is possible to prevent the high-frequency component from being excessively emphasized by the FBP method, and to suppress the high-absorber artifact.

  In this embodiment, the amount of artifact reduction is based on the amount of artifact of a tomosynthesis image reconstructed using the FBP method (hereinafter referred to as a corrected non-FBP image) as shown in the following equation (1), for example. It can be evaluated as a numerical value by indicating the percentage of reduction in the amount of artifacts in a tomosynthesis image (hereinafter referred to as a corrected FBP image) reconstructed after conversion of the measured projection data value of the superabsorbent region.

なお、本実施例のＸ線トモシンセシス装置において、被写体とは撮影対象を意味し、被検体３と、被検体３を支える寝台４とを包含する。なお、被検体３は、人体に限らず、ファントムや機械等の検査対象の物体であってもよい。

In the X-ray tomosynthesis apparatus according to the present embodiment, the subject means an imaging target, and includes the subject 3 and the bed 4 that supports the subject 3. The subject 3 is not limited to a human body, and may be an object to be inspected such as a phantom or a machine.

  Hereinafter, the X-ray tomosynthesis apparatus according to the first embodiment will be described in more detail with reference to the drawings. FIG. 1 is a diagram illustrating a hardware configuration of the X-ray tomosynthesis apparatus according to the first embodiment. As will be described later, the X-ray tomosynthesis apparatus realizes the functions of the correction processing unit 135, the superabsorbent body processing unit 136, and the image reconstruction unit 137 of the image generation unit 103 by software. FIG. 2 is a functional block diagram of an X-ray tomosynthesis apparatus realized by various types of software.

  As outlined above, the X-ray tomosynthesis apparatus of this embodiment performs input control 101 for inputting imaging conditions such as X-ray irradiation conditions and image reconstruction conditions, and controls imaging and X-ray irradiation and detection. And an imaging unit 102 that outputs measurement projection data, and an image generation unit 103 that performs correction processing, superabsorber processing, and image reconstruction on the measurement projection data that is the detected signal and outputs an image. Composed. Note that the input unit 101 and the image generation unit 103 are not necessarily configured integrally with the main body device including the imaging unit 102, and may be arranged at a location away from the imaging unit 102 and connected via a network. . In that case, the image generation unit 103 can be regarded as an independent existence as a processing device that processes the measurement projection data.

  The input unit 101 has a hardware configuration included in a general-purpose computer, and includes a keyboard 111 and a mouse 112 as input / output units, a memory 113 as a storage unit, an HDD device 115, a central processing unit 114 as a processing unit, and the like. ing. The image generation unit 103 is a data acquisition system (hereinafter referred to as DAS) 118, a memory 119 that is a storage unit, a central processing unit 120 that is a processing unit, an HDD device 121 that is a storage unit, and a display unit. A monitor 122 and the like are provided. The input unit 101 and the image generation unit 103 may be independent hardware, or may be configured to share these hardware.

  As shown in FIG. 2, the input unit 101 functions as a shooting condition input unit 131 that inputs shooting conditions. The imaging unit 102 functions as an imaging control unit 132 that controls imaging based on the imaging conditions input by the imaging condition input unit 131 and an imaging operation unit 133 that performs X-ray irradiation and detection. The image generation unit 103 includes a signal collection unit 134 that converts the detected X-ray signal into a digital signal, a correction processing unit 135 that corrects the digital signal, and converts the projection data value of the high absorber to the corrected projection data. It functions as a high-absorber processing unit 136 that processes, an image reconstruction unit 137 that reconstructs an image with respect to projection data, and an image display unit 138 that outputs a reconstructed tomosynthesis image. Of course, the signal collection unit 134 that performs AD conversion is installed in the imaging unit 102, and the imaging unit 102 can output measurement projection data as a digital signal, and the image generation unit 103 is connected via a network. In such a case, it is preferable to make such a configuration.

  As shown in FIG. 1, the input unit 101 includes a keyboard 111 and a mouse 112 in order to input shooting conditions and the like. Although not shown, other input means such as a pen tablet or a touch panel may be provided. Further, the input unit 101 includes a central processing unit (CPU) 114, a storage unit such as a memory 113 and an HDD (Hard Disk Drive) device 115, and a monitor (not shown). Each component is connected by a data bus 101a.

  Data input from the keyboard 111 or the like is transferred to the CPU 114 which is a processing unit. The CPU 114 functions as the photographing condition input unit 131 in FIG. 2 by developing and starting a predetermined program stored in advance in the memory 113, the HDD device 115, and the like. Further, the CPU 114 sends a control signal to the photographing unit 102 by developing and starting another program, and also functions as a part of the photographing control unit 132 in FIG.

  The X-ray generation unit 1 and the X-ray detection unit 2 including the X-ray generation unit of the imaging unit 102 in FIG. 1 realize X-ray irradiation and detection on the subject 3 as in a general X-ray tomosynthesis apparatus. . A typical example of the distance between the X-ray generation point of the X-ray generation unit 1 and the X-ray input surface of the X-ray detection unit 2 is 1200 [mm]. Here, the X-ray generator 1 moves relative to the subject 3 and the X-ray detector 2. An angle of the X-ray generation unit 1 with respect to the X-ray detection unit 2 when performing tomosynthesis imaging is referred to as a projection angle. If the position where the X-ray generation unit 1 and the X-ray detection unit 2 face each other is 0 degree, a representative example of the projection angle range is ± 20 degrees. A typical example of the number of projections taken by the photographing unit 102 in one tomosynthesis photographing is 60. In this case, imaging is performed once every time the X-ray generation unit 1 moves by 0.67 degrees. A typical example of the time required for tomosynthesis imaging within a projection angle range of ± 20 degrees is 10.0 [s]. The X-ray detection unit 2 includes a known X-ray detection element including a scintillator and a photodiode, and a plurality of detection elements are arranged in a two-dimensional direction in a plane parallel to the bed 4.

  For example, the number of X-ray detection elements in the X direction and the Y direction that are two-dimensionally arranged in the X-ray detection unit 2 is 2000 × 2000. A typical example of the size of each X-ray detection element is 0.2 [mm]. Each specification is not limited to the above values and can be variously changed according to the configuration of the X-ray tomosynthesis apparatus.

  The image generation unit 103 includes a processing unit including a DAS 118 and a CPU 120, a storage unit such as the memory 119 and the HDD device 121, and a monitor 122. These are connected by a data bus 103a. The DAS 118 functions as the signal collection unit 134 in FIG.

  The CPU 120 serving as a processing unit develops and activates a predetermined program stored in advance in the memory 119, the HDD device 121, etc., thereby correcting the correction processing unit 135, the superabsorbent body processing unit 136, and the image reconstruction unit in FIG. The function 137 is realized by software. In the present embodiment, at least a part or all of the superabsorbent body processing unit 136 can be realized by hardware. For example, the high-absorber processing unit 136 is configured using a custom IC such as an application specific integrated circuit (ASIC) or a programmable IC such as a field-programmable gate array (FPGA). The circuit design may be performed so as to realize the above.

  The monitor 122 functions as the image display unit 138.

  Signals detected by the X-ray detection unit 2 of the imaging unit 102 are collected by the DAS 118 functioning as the signal collection unit 134, converted into digital signals, and passed to the CPU 120. The CPU 120 performs correction and performs image reconstruction using FBP processing. Further, data is stored in the HDD device 121 or the like, and data is input / output to / from the outside as necessary. The reconstructed tomosynthesis image is displayed on a monitor 122 such as a liquid crystal display or a CRT that functions as the image display unit 138. As described above, the CPU 120, the memory 121, the monitor 122, and the like can be shared with the input unit 101.

  Next, the flow of the imaging operation of the X-ray tomosynthesis apparatus according to the first embodiment will be described with reference to the functional block diagram of FIG. 2 and the hardware configuration of FIG. 1 and the screen example of FIG. FIG. 3 is a diagram illustrating an example of the shooting condition reception screen 141 displayed on the monitor 122 of the shooting condition input unit 131.

  The imaging condition input unit 131 in FIG. 2 displays the imaging condition reception screen 141 in FIG. 3 on the monitor 122 and receives an operator input. The imaging condition reception screen 141 in FIG. 3 is an X-ray for the operator to set the tube voltage, tube current time product corresponding to the energy and output amount of X-rays to be irradiated, and the number of projections in one tomosynthesis imaging. A condition setting area 142, a reconstruction range setting area 143 for the operator to set the range of the reconstructed image, a high absorber setting area 144 for the operator to select a desired high absorbent condition, An imaging region setting area 145 for the operator to set an imaging region and an extraction method setting area 146 for the operator to select a superabsorbent extraction method are included.

  The operator operates the mouse 112, the keyboard 111, and the like while looking at the imaging condition reception screen 141, and sets the X-ray condition to the X-ray condition setting area 142 and the reconstruction range to the reconstruction range setting area 143. Desired high-absorber conditions are set in the high-absorber setting region 144, the imaging region is set in the imaging region setting region 145, and the high-absorber extraction method is set in the extraction method setting region 146. Hereinafter, setting of the imaging condition and the reconstruction condition according to the present invention will be described in more detail with reference to FIG.

  FIG. 3 shows an example in which the tube voltage value 80 [kV], the tube current time product 20 [mAs], and the number of projections 60 are set in the X-ray condition setting area 142 by the operator. FIG. 3 shows an example in which X-rays having one type of energy spectrum are used. However, in the case of multi-energy imaging using two or more types of X-rays, the operator can select tube voltage, tube current time. The items of the product and the number of times of imaging are added to the X-ray condition setting area 142 and set in the same manner for each type of X-ray.

  Further, in the reconstruction range setting area 143 of FIG. 3, the operator sets a reconstruction range (Field of View, hereinafter referred to as FOV) that is an area in which image reconstruction is performed. The reconstruction range setting area 143 in FIG. 3 is configured to set the reconstruction range by the operator setting the size and center position of the FOV. In this embodiment, as an example, the FOV is defined as a square. In the example of FIG. 3, one side of the FOV is set to 300 [mm], and the center position of the FOV is equal to the rotation center when the movement of the X-ray generator 1 is assumed to be a circular orbit, X = Y = Z = 0 [Mm] is set. However, the FOV is not limited to a square, and can be set to an arbitrary shape such as a circle, a rectangle, a cube, a rectangular parallelepiped, or a sphere. In this case as well, the configuration of this embodiment can be applied.

  In the superabsorber setting region 144 of FIG. 3, the operator sets a region extraction start point 41. As a setting method, the operator inputs a threshold value of the measurement projection data value, sets a point of the measurement projection data that is equal to or less than the input threshold value as the start point 41, and the superabsorber on the acquired measurement projection data 147. In the example of FIG. 3, a method for the operator to select the pointer 148 for a point in the region and a method for the operator to select information on the superabsorber are prepared.

  In the example of FIG. 3, specifically, the operator sets 100 or less as the threshold value of the measured projection data value. Therefore, a point indicating the measurement projection data with the threshold value 100 or less is set as the start point 41.

  In the imaging region setting region 145 of FIG. 3, the operator selects an X-ray irradiation target (a region or tissue such as the head, chest, or lung field) as an imaging region. In the example of FIG. 3, the head is selected.

  In this embodiment, as a method for extracting the region of the superabsorber, any method can be used as long as the region is extracted by expanding (or reducing) the region from the point where the region extraction is started or from the region. May be used. In addition to the region expansion method that expands the region from the start point described above, the Snakes method that extracts the region based on the initial shape, the level set method that extracts the region based on the initial value, and the initial seed (seed) A graph cut method for extracting a region can be used. In the extraction method setting region 146 of FIG. 3, the operator selects a region setting method from a known image processing technique, such as a region expansion method, a snake method, a level set method, or a graph cut method. When a method for extracting a region from a start region (start shape) instead of a start point is selected as the region extraction method, the imaging condition input unit 131 displays the high-level image data in FIG. In the absorber setting area 144, an input of a start area (start shape) may be received from an operator. Further, the imaging condition input unit 131 may accept the setting of the start point 41 from the operator in the high absorber setting region 144 and set a start region (start shape) having a predetermined shape so as to include the start point 41. .

  Note that the imaging condition reception screen 141 is not limited to the screen configuration of FIG. In addition, the X-ray conditions for accepting settings on the imaging condition reception screen 141, the reconstruction range, the superabsorber setting conditions, the imaging site setting conditions, and the extraction method are stored in advance in the HDD 115, and the imaging condition input unit 131 It is also possible to read the setting conditions from the HDD device 115. In this case, it is not necessary for the operator to input X-ray conditions and the like every time. It is also possible to store a plurality of types of combinations of the setting conditions in advance so that the operator can select from a plurality of types.

  Next, the imaging unit 102 in FIG. 2 performs tomosynthesis imaging according to the imaging conditions received by the imaging condition input unit 131 from the operator. When the operator instructs the start of imaging using the mouse 112, the keyboard 111, or the like, the CPU 114 outputs to the detector controller 116 and the X-ray controller 117 of the imaging controller 132. In response to the control signal, the X-ray generation unit 1 is controlled to move in the body axis direction, and the imaging region of the subject 3 is the X-ray passage range between the X-ray generation unit 1 and the X-ray detection unit 2, that is, The movement of the X-ray generator 1 is stopped at the time when it coincides with the imaging position. Thereby, the arrangement of the subject 3 at the imaging start position is completed.

  Further, the X-ray controller 117 starts the movement of the X-ray generation unit 1 via the drive motor at the same time when the CPU 114 instructs to start imaging. When the movement of the X-ray generation unit 1 enters a constant speed state and the placement of the subject 3 at the imaging position is completed, the CPU 114 causes the X-ray controller 117 to transmit the X-ray generation timing of the X-ray generation unit 1. And the imaging timing of the X-ray detector 2 is instructed. The X-ray controller 117 irradiates X-rays from the X-ray generator 1 according to this instruction, and the X-ray detector 2 detects X-rays and starts imaging. The X-ray controller 117 determines the energy spectrum and output amount of the X-rays to be irradiated, for example, based on the tube voltage and tube current time product of the X-ray generator 1 set by the operator.

  Although an example using X-rays having one type of energy spectrum has been described here, the configuration of this embodiment can also be applied to tomosynthesis for multi-energy imaging. In that case, for example, the tube voltage is switched at high speed for each movement or during one movement, and X-rays having two or more types of energy spectra are irradiated to control to acquire imaging data.

  The signal collection unit 134 of the image generation unit 103 converts the output signal of the X-ray detection unit 2 into a digital signal and stores it in the memory 119. For this data, the correction processing unit 135 performs correction such as offset correction for calibrating the zero value of the X-ray detection signal and known air calibration processing for correcting the sensitivity between the detection elements. Acquire measurement projection data. The measurement projection data is sent to the high-absorber processing unit 136 and the image reconstruction unit 137.

  In FIG. 4, the further detailed functional structure of the superabsorbent body process part 136 of a present Example is shown. As described above, the superabsorber processing unit 136 realized by software or the like includes the three-dimensional material search unit 151, the two-dimensional material search unit 152, and the extraction region conversion that converts the measurement projection data value of the region of the high absorber. Part 153.

The three-dimensional material search unit 151 obtains a three-dimensional region using the three-dimensional region expansion method using the start point 41 received under actual imaging conditions, and sets the start point in the two-dimensional measurement projection data for each projection angle. Set. Therefore, a three-dimensional differentiation processing unit 161 that performs a three-dimensional differentiation process on three-dimensional measurement projection data in which two-dimensional measurement projection data for each projection angle are arranged in the projection angle direction, and a gradient image acquired by the differentiation process On the other hand, a three-dimensional boundary determination unit 162 that determines a threshold a _3D or more as a boundary, and a three-dimensional region expansion unit 163 that expands the region to satisfy the inside of the boundary based on the setting received on the imaging condition reception screen 141 are provided. ing.

On the other hand, the two-dimensional material search unit 152 extracts a superabsorbent region based on the start point set by the three-dimensional material search unit 151 using, for example, a two-dimensional region expansion method based on boundary extraction. Therefore, the two-dimensional substance search unit 152 performs a threshold a _2D on the two-dimensional differentiation processing unit 164 that performs the two-dimensional differentiation process on the measurement projection data of the projection angle and the gradient image acquired after the differentiation process. A two-dimensional boundary determination unit 165 that determines the above as a boundary and a two-dimensional region expansion unit 166 that expands the region so as to satisfy the inside of the boundary from the start point and extract the region are provided.

  Next, the extraction region conversion unit 153 has a function of converting the measurement projection data of the extracted region into a value that hardly causes artifacts (measurement projection data value when the X-ray absorption rate is lower than that of the high absorber). .

  Each of these functional blocks operates as shown in the flowchart of FIG. Details will be described below. First, the three-dimensional differentiation processing unit 161 will be described.

  In the three-dimensional differentiation processing unit 161, the two-dimensional measurement projection data arranged in the order of the detector numbers in the horizontal direction x and the vertical direction y detected by the X-ray detection unit 2 in step 171 of FIG. For f (x, y, z) that is three-dimensional measurement projection data (three-dimensional sinogram) arranged in the projection angle direction θ = z, as shown in the following equation (2), for example, by a known image processing technique. A gradient image ▽ f (x, y, z) is calculated by performing partial differential calculation in a certain three-dimensional direction.

式（２）の▽ｆ（ｘ、ｙ、ｚ）は、ｆ（ｘ、ｙ、ｚ）の勾配を示す。ここで、第３項（ｕｚ）の前に係る係数αは、投影枚数（投影角度間隔）によって決まる係数であり、一般に投影角度間隔が大きいほど大きくなる。原点は、撮影開始後の１投影目における正面左上の検出器とする。ｕｘ、ｕｙは、横方向および縦方向における検出器番号の単位ベクトルを示す。ｕｚは、投影角度方向の単位ベクトルを示す。式（２）は、３×３×３検出器内の近傍６検出器素子の値を用いて測定投影データの勾配画像を算出しているが、測定投影データのＳ／Ｎに応じて、例えばノイズが大きい場合は近傍１８検出器素子の値を用いて勾配画像を算出してもよい。

In the equation (2), ▽ f (x, y, z) indicates the gradient of f (x, y, z). Here, the coefficient α related to the third term (uz) is a coefficient determined by the number of projections (projection angle interval), and generally increases as the projection angle interval increases. The origin is the detector at the upper left of the front in the first projection after the start of imaging. “ux” and “uy” indicate unit vectors of detector numbers in the horizontal direction and the vertical direction. uz indicates a unit vector in the projection angle direction. Equation (2) calculates the gradient image of the measurement projection data using the values of the six neighboring detector elements in the 3 × 3 × 3 detector, but according to the S / N of the measurement projection data, for example, If the noise is large, the gradient image may be calculated using the values of the neighboring 18 detector elements.

Next, in the three-dimensional boundary determination unit 162, the gradient image ▽ f (x, y, z) acquired after the partial differential calculation in step 172 of FIG. The threshold a _3D or more is set as the boundary pixel b (x, y, z) = 1, and the threshold a less than _3D is set as the boundary pixel b (x, y, z) = 0. As a result, as shown in FIG. 4B, the pixel value of the pixel at the position (boundary) where the measurement projection data changes sharply at the boundary between the measurement projection data of the high absorber and the surroundings is 1, and the high absorption body The pixel inside the pixel and the pixel outside the superabsorber become zero.

  Next, in the three-dimensional region expansion unit 163, since the start point 41 set by the operator in step 173 in FIG. 5 is set inside the superabsorbent, the X-ray detection unit starts from the start point 41. The area is expanded in two horizontal directions, vertical directions, and projection angle directions. Specifically, with respect to the pixel b (x, y, z) = 0 at the start point 41, it is determined as a high absorber only when the value of the adjacent pixel is 0, and b (x, y, z) Change to = 2. Next, it is determined whether the pixel further adjacent to the pixel of the superabsorber changed to b (x, y, z) = 2 is a superabsorber, and if the value of the adjacent pixel is 0, b ( x, y, z) = 2. This process is repeated in the three-dimensional direction until the determination target pixel is not present (FIG. 4C). Thereby, the three-dimensional region 42 of the pixel b (x, y, z) = 2 located inside the boundary of the high absorber can be extracted.

  The three-dimensional region expansion unit 163 obtains a range that the extracted three-dimensional region 42 occupies in the two-dimensional measurement projection data at a projection angle other than the projection angle at which the start point 41 is set, and 1 within the range The above point is set as the start point 43 in the two-dimensional measurement projection data of the projection angle.

  Next, based on the start point 43 set in the three-dimensional region expansion unit 163, the two-dimensional material search unit 152 extracts the superabsorbent region from the two-dimensional measurement projection data at each projection angle. Specifically, the two-dimensional differentiation processing unit 164 performs two-dimensional measurement projection data g in the horizontal direction x and the vertical direction y at a certain projection angle z as shown in the following equation (4) in step 174 of FIG. A gradient image ▽ g (x, y, z) is calculated by, for example, performing a partial differential calculation in a two-dimensional direction, which is a known image processing technique, on (x, y, z).

Next, in the two-dimensional boundary determination unit 165, in step 175 of FIG. 5, the gradient image に g (x, y, z) acquired after the partial differential calculation of the projection angle is expressed as shown in Expression (5). The boundary image e (x, y, z) = 1 is set to be _{equal to} or greater than a predetermined threshold a _2D , or the boundary image e (x, y, z) = 0 is set to be less than the threshold a _2D .

  Next, in the two-dimensional area expansion unit 166, based on the start point 43 set by the three-dimensional material search unit 151 in step 176 of FIG. Extend the region vertically. At this time, with respect to the pixel e (x, y, z) = 0 as the starting point, it is determined as a high absorber only when the value of the adjacent pixel is 0, and e (x, y, z) = 2. change. Similarly, a pixel adjacent to the determined superabsorber pixel is determined, and the process is repeated until a condition in which there is no determination target pixel is reached. By the processing of the two-dimensional material search unit 152, the high-absorber region 44 of the measurement projection data can be extracted at each projection angle. Thereby, the superabsorber region 44 that is inside the boundary between the measurement projection data of the superabsorber and the surroundings can be extracted with high accuracy.

  As described above, in the present embodiment, the reason why the process of the three-dimensional substance search unit 151 and the process of the two-dimensional substance search unit 152 are executed in stages will be described. In the present embodiment, first, in the three-dimensional differentiation process of the three-dimensional material search unit 151, the gradient image is calculated from the total value (formula (2)) in the three directions of the x, y, and z directions, thereby obtaining the three-dimensional region 42. Therefore, the region 42 can be set for the measurement angle data of other projection angles from the start point 41 set for the measurement projection data of one projection angle. However, when the absorption value difference is significantly large in the z direction that is the projection angle, the pixel is likely to be determined as a boundary. Due to this influence, the process of the three-dimensional material search unit 151 may estimate the high absorber region smaller by the amount of absorption value difference in the z direction than the two-dimensional differentiation process of the two-dimensional material search unit 152. . Therefore, in order to extract the high-absorber region with high accuracy, after the high-absorber region is extracted from the measurement projection data of the entire projection angle by the three-dimensional material search unit, By performing, the region 44 can be extracted with high accuracy.

  Next, in the extraction region conversion unit 153, in step 177 of FIG. 5, the extracted projection region obtained by expanding the region is converted into a representative superabsorbent measurement projection data value c as shown in Expression (6). The difference (f (x, y, z) −c) times d is added and converted to measurement projection data f ′ (x, y, z). The coefficient d used for the conversion is set to d = 1/10 in order to sufficiently reduce the influence of the artifact. Thereby, it is possible to convert the measurement projection data value in the region 44 of the high absorber into the measurement projection data value when the X-ray absorption rate is lower than that of the high absorber without using the values in the peripheral region.

  The measured projection data value c of a typical superabsorber includes the imaging conditions and reconstruction conditions, the position (x, y, z) of the subject in the three-dimensional space, and the position of the superabsorber (x, y, z). ) And information such as size. In addition, there is a method of estimating by interpolation from the value of the peripheral region. However, since the distance from the peripheral region increases as the size of the superabsorber increases, there is a problem that the accuracy of the value by interpolation decreases.

  The conversion process to the specific value will be described in detail with reference to FIG. FIG. 6 shows projection data 401 and a reconstructed tomosynthesis image 402. In FIG. 6, a white area has a large projection data value, a black area has a small projection data value, and an intermediate area is indicated by a gray scale represented by gray shades. For example, the measurement projection data 405 is obtained by photographing a phantom in which a high absorber 404 is inserted inside a sphere 403. The projection data 406 of the superabsorbent body 404 extracted by performing the processing of the three-dimensional substance search unit 151 and the two-dimensional substance search unit 152 on the measurement projection data 405 is shown. Next, when the high-absorber 404 shown in the high-absorber projection data 406 is converted into a specific value f ′ (x, y, z) by the extraction region conversion unit 153, the high-absorber conversion projection data 407 is obtained. can get. Finally, a well-known log transformation process and image reconstruction are performed on the high-absorber transformation projection data 407 to obtain a reconstructed image 409. At this time, the magnitude of the value is inverted by the log conversion process. By compressing the value by the conversion process to the specific value f ′ (x, y, z), the value of the superabsorbent body 410 is lowered, and the artifact component is reduced.

  As a configuration different from that of FIG. 6 for realizing the first embodiment, the configuration of FIG. 7 will be described. In FIG. 6, only the conversion process to the specific value is performed, but in FIG. 7, the well-known log conversion process and image reconstruction are performed on the high-absorber projection data 406, and the high-absorber reconstructed image is obtained. 411 is acquired. At this time, the line-shaped artifact 413 generated from the high-absorber 412 is removed by a known threshold process or a feature extraction algorithm by using a property having different shapes or pixel values, and an image of the high-absorber 412 is obtained. Extract only. Next, for only the extracted region of the high absorber 412, for example, the value of the high absorber 414 shown in the reconstructed image 409 is increased by multiplying the inverse of the coefficient d used in the conversion process to the specific knowledge. Restore accuracy. At this time, it is not necessary to accurately obtain the pixel value of the superabsorbent body reconstructed image 411. If at least the region of the superabsorbent 412 can be extracted, the value of the superabsorber 414 can be restored by multiplying the inverse of the uniform coefficient d. Compared with the method of reconstructing the entire area by adding data by reducing the data size of the superabsorbent body reconstructed image 411 due to the effect of limiting the area, or by reducing the display byte by binarizing the pixel value, etc. Thus, a reduction in memory can be realized.

  FIG. 8 shows a configuration further different from those in FIGS. 6 and 7 for realizing the first embodiment. In FIG. 8, the conversion processing of the specific value f ′ (x, y, z) is not performed, the reconstructed image 409 is reconstructed from the measurement projection data 405, and the difference from the above-described line-shaped artifact 413 is obtained. Artifacts 413 on the line are removed, and a corrected image 415 is acquired. Specifically, only the artifact 413 is extracted from the superabsorbent reconstructed image 411 by using a known threshold process, a feature extraction algorithm, or the like using a property having different shapes or pixel values. Next, by taking a difference from the reconstructed image 409 for only the extracted artifact 413, the value of the high absorber 416 shown in the corrected image 415 can be restored with high accuracy.

  As described above, the conversion of the projection data value of the high absorber included in the certain projection angle z-th measurement projection data has been described, but the conversion process is similarly performed on the measurement projection data of other projection angles.

  The image reconstruction unit 137 performs reconstruction using the FBP method on the measurement projection data of the entire projection angle, and can reduce artifacts generated from the high absorber due to specific absorption value conversion.

  Note that the region expansion method described above is an example, and may be applied to other methods such as graph cut, level set, and snakes methods, which are known image processing techniques.

  In order to verify the effectiveness of this example, as shown in FIG. 9, a phantom simulation was performed in which a high-absorber was simulated inside spherical water having a diameter of 150 [mm]. Each cross section in FIG. 9 represents a Coronal plane 181, a Sagittal plane 182, and an Axial plane 183. The ratio of the X-ray absorption coefficient between water and the superabsorber is 1:30, and a spherical superabsorber with a diameter of 10 [mm] in the X and Y directions of the Coronal surface 181 is 25 [mm] and 50 [mm], respectively. Placed in a separate position. The spherical phantom is a position where the rotation center when the movement of the X-ray generation unit 1 is assumed to be a circular orbit is 0 [mm] and is shifted from the X-ray detection unit 2 to the X-ray generation unit 1 by 100 [mm]. (Z = 100 [mm]). Z = 0 mm is the position of the detection surface of the X-ray detection unit 2.

  FIG. 10 shows the result of creating measurement projection data from the phantom shown in FIG. 9 by simulating the geometric system of the X-ray generator 1 and the X-ray detector 2. X-rays do not assume energy and do not include the effects of X-ray quantum noise, circuit noise, and scattered radiation. Each of the cross sections in FIG. 10 includes the measurement projection data 184 of the X-ray detection unit 2 having a projection angle of 0 degrees out of the projection angle ± 20 degrees, the cross section 185 in the projection angle direction in the X direction, and the cross section in the projection angle direction in the Y direction. 186. On the measurement projection data 184 with a projection angle of 0 degrees, a pointer is set at the center of each superabsorber, and the region of the superabsorber is expanded to the entire projection angle by steps 171 to 177 shown in FIG.

  FIG. 11A shows a corrected FBP image, and FIG. 11B shows a corrected FBP image. Each cross section of FIG. 11A and FIG. 11B represents a Coronal surface 181, a Sagittal surface 182, and an Axial surface 183.

  It can be seen that the corrected FBP image was able to reduce black artifacts around the superabsorber compared to the uncorrected FBP image. Thus, it was shown that the tomosynthesis image which achieved the artifact reduction of the high absorber can be acquired by the method of the present embodiment.

  In this embodiment, the pixel value of the extracted high-absorber is converted into a specific value f ′ (x, y, z) that is less affected by artifacts, but the measurement projection data of only the high-absorber is separated from the measurement projection data. Then, the image reconstruction unit 137 may perform image reconstruction. At this time, the image reconstruction unit 137 needs to add a high-absorber and a reconstructed image other than the high-absorber.

  In this embodiment, the X-ray detection unit 2 at a fixed position is used. However, the present invention is also applicable to a method in which imaging is performed while the X-ray detection unit 2 moves in synchronization with the movement of the X-ray generation unit 1. .

  In the present embodiment, the tomosynthesis image is reconstructed using the measurement projection data acquired from one tomosynthesis imaging, but is not limited to once, for example, measurement projection data at different times by two or more imaging. It is also applicable to reconstruction using

  Furthermore, in this embodiment, an X-ray tomosynthesis apparatus for living body is shown as an example, but the configuration of this embodiment is applied to an X-ray tomosynthesis apparatus or laminography apparatus for non-destructive inspection such as explosives inspection and product inspection. Of course it is also possible to do.

  Next, Example 2 will be described. As shown in FIG. 12, the X-ray tomosynthesis apparatus according to the second embodiment basically has the same configuration as the X-ray tomosynthesis apparatus according to the first embodiment, and further has a region of the superabsorber 195 having an adjacent projection angle. And a three-dimensional interpolation processing unit 168 that interpolates between the high-absorbers 195 of the measured projection data at adjacent projection angles when they are not connected. ing. Hereinafter, the second embodiment will be described focusing on the configuration different from the first embodiment.

  FIGS. 13A and 13B show a cross section 185 in the projection angle direction in the X direction as in FIG. 10, and assume a background 193, air 194, and high absorber 195. FIG. 13A shows a state in which the superabsorbers with adjacent projection angles are not connected. The three-dimensional interpolation determination unit 167 determines whether or not the superabsorbent region shown in FIG. In this example, since it is determined that there is no connection, the three-dimensional interpolation processing unit 168 performs interpolation processing using surrounding measurement projection data as shown in FIG.

  As described above, in the second embodiment, in the three-dimensional measurement projection data f (x, y, z), as shown in FIG. 13A, the region of the high absorber 195 having a certain projection angle is adjacent to the projection. It is determined whether or not it is connected to the area of the angular superabsorber 195, and if not connected, interpolation processing is performed to virtually connect. As a result, even when the region of the high absorber 195 is separated between adjacent projection angles, and the search of the region of the high absorber in the three-dimensional measurement projection data cannot be performed in the three-dimensional material search unit 151, the measurement projection data after interpolation is obtained. By using it, it becomes possible to search the region of the superabsorber.

  The three-dimensional interpolation determination unit 167 estimates the region of the superabsorber 195 from the imaging conditions and the subject to determine the connection state (1), and the three-dimensional substance search unit 151 extracts the region of the superabsorber. It is configured to perform any one of the methods (2) for determining by performing.

  In the former (1) estimation method, the projection angle of the X-ray generator 1, the distance from the X-ray generator 1 to the X-ray input surface of the X-ray detector 2, and the position (x, y, The region of the superabsorber in the projection angle direction is obtained from z) and the size, and the presence or absence of connection of the region of the superabsorber is geometrically estimated. Concatenation represents the adjacency relationship between pixels indicating the same superabsorber on the measurement projection data.

  In the search method of the latter (2), as shown in FIG. 13, the three-dimensional substance search unit 151 extracts the superabsorbent region as described in the first embodiment, and connects the projection angle directions based on the extraction result. Determine. Concatenation means that pixels indicating the same superabsorber are connected on the measurement projection data. The determination criteria refer to the extracted high-absorber region, and the high-absorber region extracted in the projection angle direction is not interrupted at an intermediate projection angle.

  At this time, when the three-dimensional interpolation determination unit 167 determines that there is a connection, the processing of the three-dimensional material search unit 151 of the first embodiment is performed without performing the interpolation processing of the three-dimensional interpolation processing unit 168.

  When the three-dimensional interpolation determination unit 167 determines that there is no connection, interpolation processing is performed using surrounding measurement projection data, and measurement projection data with connection virtually is created as shown in FIG. At this time, for the interpolation process, for example, a method of generating an interpolation area using an average value of measured projection data of the same detector at the front and rear projection angles, which is a known technique, can be used.

  The region of the superabsorber after the interpolation in FIG. 13B is continuous with the superabsorber region in the projection angle direction. Therefore, the three-dimensional region expansion unit 163 has a high absorption without interruption in the projection angle direction. Extract body regions. The measurement projection data interpolated by the three-dimensional interpolation processing unit 168 is not necessarily used after the two-dimensional material search unit 152, and may be excluded from the memory in the apparatus from the viewpoint of reducing the data size.

  Next, Example 3 will be described. In the third embodiment, as shown in FIG. 13A shown in the second embodiment, when the areas of the high-absorber bodies having the adjacent projection angles are not connected and the measurement projection data between the projection angles cannot be searched, Using the pattern recognition, the superabsorber region is extracted based on the position information estimated from the measured projection data of the front and rear projection angles.

  The X-ray tomosynthesis apparatus of this embodiment basically has the same configuration as that of the X-ray tomosynthesis apparatus of Embodiment 1, and further includes a three-dimensional pattern recognition determination unit 169 and three-dimensional pattern recognition processing as shown in FIG. A three-dimensional pattern recognition unit 155 including a unit 170.

  The three-dimensional pattern recognition determination unit 167 determines whether or not the measurement projection data for the projection angle can be searched using the same process as the three-dimensional interpolation determination unit 167 in the second embodiment. If the search is impossible in the three-dimensional pattern recognition processing unit 170, as shown in FIG. 15A, at least the shape and pixel value of the superabsorbent region 191 in the measured projection data at the representative n-th projection angle. Based on one, using a known pattern recognition method such as similarity search, a high-absorber region 192 of the measured projection data of the (n + 1) th projection angle is extracted as shown in FIG. . At this time, the three-dimensional pattern recognition processing unit 170 uses the a priori information such as the photographing condition, the reconstruction condition, and the position (x, y, z) of the subject in the three-dimensional space to measure the measurement projection data of the front and rear projection angles. Therefore, the amount of movement of the superabsorber can be estimated and the accuracy of pattern recognition can be improved.

  Next, Example 4 will be described. The X-ray tomosynthesis apparatus according to the fourth embodiment basically has the same configuration as that of the X-ray tomosynthesis apparatus according to the first embodiment. Further, as shown in FIG. A parameter optimization unit 201 for searching for a three-dimensional substance is provided that determines a result of body extraction and optimizes a parameter for searching for a three-dimensional substance. Also for the two-dimensional substance search unit 152, a two-dimensional substance search parameter optimization unit 202 that determines the extraction result of the superabsorber and optimizes the two-dimensional substance search parameter is added. Hereinafter, the present embodiment will be described focusing on the configuration different from the first embodiment.

  The three-dimensional material search parameter optimization unit 201 of the three-dimensional material search unit 151 of the present embodiment will be described with reference to FIG.

In the three-dimensional substance search parameter optimization unit 201, as shown in FIG. 17A, the extraction result of the region of the superabsorbent selected using the parameter threshold value a _3D 212 of the start point 211 is inappropriate. As shown in FIG. 17 (b), the area of the superabsorbent region is too large, the area of the superabsorbent region shown in FIG. 17 (c) is too small, or the area of the superabsorbent region is too small. As shown in d), there are three types when there is no continuity in the region of the superabsorber between projection angles. That is, FIG. 17B is an example in which the superabsorber region 221 is excessively extracted from the true superabsorber region. The area of the true region serving as the determination criterion can be estimated from the area and volume of the superabsorber having a known shape. FIG. 17C shows an example in which the superabsorber region 222 is extracted too little from the true superabsorber region. FIG. 17D shows the result of calculating the areas of the projection angles N−2, N−1, N, and N + 1, for example, with respect to the true superabsorbent region, and as a result, only some projection angles N are excessive. It is the result of extracting the superabsorbent region 221.

In Example 4, the absolute value difference 223 (vertical axis in FIG. 17A) of the estimated true value and the total area of the region of the superabsorbent is obtained, and when the absolute value difference 223 exceeds the specified value 224, the parameter Reset the threshold a _3D 212. As a resetting method, for example, a known bisection method is used, after the magnitude of the threshold value a _3D 212 is greatly changed, a parameter threshold value a _3D close to a predetermined value is selected, and the parameters are successively narrowed down. . When the absolute value difference 223 obtains a value 225 that is lower than the specified value 224, the process of the three-dimensional substance search parameter optimization unit 201 illustrated in FIG. 16 ends.

The two-dimensional substance search parameter optimization unit 202 optimizes the parameter threshold a _2D using the same process as that of the above-described three-dimensional substance search parameter optimization unit 201.

  Next, Example 5 will be described. In the first embodiment, the high-absorber processing unit 136 has been described with respect to the configuration for extracting the high-absorber from the measurement projection data. The measurement projection data indicates the measurement value of the X-ray absorbed by the subject based on the irradiation X-ray, as shown in Expression (7), and the measurement projection data fi (x, y, z) of only air is the subject. Is represented using the position λ (j) of the space where the X-ray exists and the path length l connecting the X-ray generation unit 1 and the X-ray detection unit 2.

  In the fifth embodiment, either the measurement projection data or the measurement projection data after log conversion is measured according to the measurement projection data and the conditions set in the high-absorber setting region 144 of the imaging condition reception screen 141. Using the selected measurement projection data, the three-dimensional material search unit 151 performs a process of extracting the superabsorbent region.

  The measurement projection data after the log conversion includes the measurement projection data fi (x, y, z) of only air and the measurement projection data f (x, y, z) after transmission of the subject, as shown in Expression (8). It is expressed as a percentage.

  The X-ray tomosynthesis apparatus according to the fifth embodiment basically has the same configuration as that of the X-ray tomosynthesis apparatus according to the first embodiment. In this case, a log conversion determination unit 156 including a processing unit 232 that performs log conversion on the measurement projection data is provided. Hereinafter, the fifth embodiment will be described focusing on a configuration different from the first embodiment.

The Log conversion determination processing unit 231 and the Log conversion processing unit 232 of the Log conversion determination unit 156 according to the fifth embodiment will be described with reference to FIG. In FIG. 19, the horizontal axis represents the integral value of the absorption value of the subject in each measurement projection data. The vertical axis in FIG. 19 (a) shows the measured projection data f (x, y, z) after passing through the subject, and the vertical axis in FIG. 19 (b) shows the measured projection data y (x, y, z after log conversion). ). In FIG. 19A, there are two types of superabsorbers 241 and 242 having different absorption values. Since the measured projection data f (x, y, z) 244 and 245 have different values with respect to the range 243 before and after the two types of absorption values, a difference Δf (x, y, z) occurs between them. . When the difference Δf (x, y, z) is greater than or equal to a certain value Th, processing is difficult with the same threshold parameter a _3D 212 of the three-dimensional material search unit 151.

On the other hand, FIG. 19B shows measured projection data after Log conversion. In FIG. 19B, there are two types of high-absorbers 246 and 247 having different absorption values. Since the difference between the measurement projection data y (x, y, z) 248 and 249 is very small with respect to the range 243 before and after the two types of absorption values, the same threshold parameter a _3D 212 can be used.
Also in the two-dimensional material search unit 152, the presence / absence of log conversion may be determined and processed in the same manner as the above-described three-dimensional material search unit 151.

  Next, Example 6 will be described. In the fifth embodiment, either the measurement projection data or the measurement projection data after log conversion is selected, and the substance search unit 151 extracts the region of the high absorber. In the sixth embodiment, in addition to the configuration of the fifth embodiment, in the three-dimensional material search unit 151 and the two-dimensional material search unit 152, irradiation X-ray and detection X-ray signal versus noise are used for boundary determination and region expansion processing. In view of the influence of the amount (hereinafter referred to as SN), a noise reduction filter is further applied to reduce the amount of noise.

  When the measurement projection data f (x, y, z) is used as the noise reduction filter, the square root √ (f (x, y, z)) of the signal can be approximated as noise, so each f (x, y , Z), a known average filter weight w = 1 / (f (x, y, z) / √ (f (x, y, z))) is applied. The lower the SN, the greater the weight w and the higher strength average value filter is applied. On the other hand, when the measurement projection data y (x, y, z) after Log conversion is used, the weight may be Log (w).

  Next, Example 7 will be described. In the first embodiment, the image reconstruction unit 137 uses the FBP method to generate a reconstructed image. However, in the seventh embodiment, the image reconstruction unit 137 uses the FBP method to perform reconstruction. An updated image is obtained using an image as an initial value and successive approximation reconstruction. At this time, the pixel value of the reconstructed image is brought close to the true value by introducing a non-negative condition that constrains that there is no absorption value below air. Furthermore, in this embodiment, the non-negative condition is changed for each update count, and the convergence speed is increased while maintaining the image quality (spatial resolution, contrast, etc.) of the reconstructed image within a certain calculation time.

  The X-ray tomosynthesis apparatus of the seventh embodiment basically has the same configuration as that of the X-ray tomosynthesis apparatus of the first embodiment, and the reconstructed image acquired by the FBP method is stored in the image reconstruction unit 137 as an initial value. In addition, a processing unit that acquires an image updated using successive approximation reconstruction and a processing unit that changes a non-negative condition during the update are added. Hereinafter, the seventh embodiment will be described focusing on a configuration different from the first embodiment.

  As shown in FIG. 20, the image reconstruction unit 137 includes an analytical reconstruction unit 301, a non-negative condition parameter storage unit 302, a forward projection processing unit 303, a difference processing unit 304, and a back projection processing unit 305. A successive approximation reconstruction unit 200 including a conditional image correction unit 306.

  In the image reconstruction unit 137, the analytical reconstruction unit 301 reconstructs a tomosynthesis image by the FBP method. The tomosynthesis image is used as an initial image, and the non-negative condition parameter storage unit 302 searches for the minimum pixel value from the initial image, for example, and stores it as a non-negative condition parameter. Next, the forward projection processing unit 303 obtains calculated projection data by performing projection calculation on the initial image in the forward direction (hereinafter referred to as forward projection calculation). The difference processing unit 304 obtains a difference (corrected projection data) between the calculated calculation data and the measured projection data, and the back projection processing unit 305 back-projects the corrected projection data to generate a corrected image. The conditional image correction unit 306 corrects (updates) each pixel of the tomosynthesis image using the corrected image. If the updated pixel value is smaller than the non-negative condition parameter value described above, Do not update the value. On the other hand, if it is larger than the non-negative condition parameter, the pixel value is updated according to the reconstruction algorithm. This is repeated until a predetermined number of updates. The number of repetitions is predetermined.

  As the non-negative condition parameter for each update count described above, the minimum value is used as an example, but an optimal value corresponding to the pixel value or pixel position in the updated image may be calculated.

  The operation of each part in FIG. 20 will be described in more detail using the flow in FIG.

  As an algorithm for correcting an image, a known sequential reconstruction method can be used. Here, as an example, a case where an SPS (Separable-Paraboloidal-Surrogate) method is used will be described.

The analytical reconstruction unit 301 uses a known analytical reconstruction method such as the Feldkamp method to calculate the tomosynthesis image λ ^{k =} from the measurement projection data y (i) corrected by the correction processing unit 135 and the high absorber processing unit 136. ⁰ (j) is obtained (step 311). Note that k is an integer greater than or equal to 0 indicating the number of repetitions (update count) of sequential reconstruction, and k = 0 indicates an initial image. Further, j is a pixel number, and λ ^k (j) indicates the pixel value of the pixel j of the image whose update count is k times.

  Next, the tomosynthesis image is searched, and for example, the minimum pixel value is stored as a non-negative condition parameter (step 319). By introducing a non-negative condition parameter, image quality can be improved by introducing a pixel value constraint that is higher than air for artifacts that are essentially lower than air, compared to the case where there is no non-negative condition. On the other hand, as will be described later, the image quality (spatial resolution and contrast) of the reconstructed image within a fixed calculation time can be compared with the conventional method of converting to a constant value by updating the non-negative condition parameter according to the updated image. Etc.), the convergence speed can be increased. This is because there is a case where a constant value is converted into a constant value or low frequency component region even in a region where a high frequency component structure originally exists. By changing the non-negative condition during the update according to the present invention, there is an effect of avoiding an excessive decrease in the frequency component and sequentially converging the pixel value to the true value.

なお、Ｌは、総画素数である。ｉは、検出素子の番号を示し、Ｉは、総検出素子数である。なお、この逐次再構成法は、一般的な２次元（ｘ、ｙ方向）の断層像だけでなく、１次元データ（ｘ方向）、体軸方向ｚに像を重ねあわせた３次元データ（ｘ、ｙ、ｚ方向）、また、さらに時間方向ｔを考慮した４次元データ（ｘ、ｙ、ｚ、ｔ）にも適用可能である。 In the SPS method, a tomosynthesis image λ ^{k + 1} (j) whose number of corrections is (k + 1) times is expressed by the following equation (9) using ^k tomosynthesis images λ ^k (j).

Note that L is the total number of pixels. i indicates the number of detection elements, and I is the total number of detection elements. Note that this sequential reconstruction method is not only a general two-dimensional (x, y direction) tomographic image, but also one-dimensional data (x direction), and three-dimensional data (x , Y, z direction), and further, it can be applied to four-dimensional data (x, y, z, t) considering the time direction t.

Hereinafter, the sequential reconstruction process according to the equation (9), that is, the process of correcting the tomosynthesis image λ ^k (j) with the number of updates k and calculating the tomosynthesis image λ ^{k + 1} (j) with the number of corrections (k + 1). I do.

  The conditional image correction unit 306 performs the following processing (steps 312 to 317 and 319) until the number of repetitions (number of updates) reaches a predetermined number.

式（１０）において、ｌは、修正対象の画素ｊとｉ番目の検出素子（検出素子ｉ）とを結ぶライン上にあるＬ個の画素の番号を表す。Ｃ（ｉ、ｌ）は、画素ｌが検出素子ｉに寄与する割合を表す。なお、Ｃ（ｉ、ｌ）の値は、検出素子の位置や順投影計算、または逆投影計算の手法によって異なる値が設定される。 The forward projection processing unit 303 performs forward projection processing on the pixels of the tomosynthesis image λ ^k (j) to obtain calculated projection data S (i) (step 313). The calculated projection data S (i) is obtained by calculating the following equation (10).

In Expression (10), l represents the number of L pixels on the line connecting the correction target pixel j and the i-th detection element (detection element i). C (i, l) represents the ratio at which the pixel l contributes to the detection element i. Note that the value of C (i, l) is set differently depending on the position of the detection element, the forward projection calculation, or the back projection calculation method.

The difference processing unit 304 subtracts the calculated projection data S (i) from the measured projection data y (i) according to the following equation (11) to obtain corrected projection data Δy ^k (i) (step 314).

The back projection processing unit 305 performs back projection processing on the corrected projection data Δy ^k (i) according to the equation (12) to generate a corrected image Δλ ^k (j) (step 315).

The conditional image correction unit 306 calculates the following equation (13) to subtract the pixel value of the corrected image Δλ ^k (j) from the pixel value of the tomosynthesis image λ ^k (j), thereby correcting the corrected tomosynthesis image λ. ^{k + 1} (j) is obtained, and the (k + 1) -th image is obtained (number of updates) (step 316). However, when the pixel value of the tomosynthesis image λ ^k (j) to be corrected is equal to or less than the non-negative condition parameter stored in the non-negative condition parameter storage unit 302, the pixel value is not updated.

  When the conditional image correction unit 306 obtains the number of repetitions (update count) (k + 1) -th image, the correction count k is incremented by 1 (step 317), and the process returns to step 319 to match the updated image with the non-negative condition parameter. Update. By updating the non-negative condition parameter in this way, the image quality (spatial resolution, contrast, etc.) of the reconstructed image within a certain calculation time is maintained as compared with the conventional method of converting to a constant value at a time. The convergence speed can be increased.

Next, the process proceeds to step 312, and the processes of steps 313 to 317 and 319 are repeated until the number of corrections k after the increment becomes equal to the number of corrections K set in advance. As a result, the above-described processing is repeatedly performed until the number of corrections k after the increment becomes equal to the preset number of corrections K. When the number of corrections k reaches K, the tomosynthesis image obtained by the image display unit 138 is obtained. The tomosynthesis image λ ^k (j) is displayed on the monitor 122.

  The tomosynthesis apparatus described in Examples 1 to 7 described above can also be expressed as follows.

(1) An X-ray generation unit that generates X-rays according to the set imaging conditions, an X-ray detection unit that detects the X-rays that have passed through a subject and obtains measurement projection data, and the X-ray generation unit And an X-ray detection unit, an imaging unit having a mechanism for moving around the subject, a substance extraction unit for extracting a substance having a specific X-ray absorption coefficient from the measurement projection data from the imaging unit, An image generation unit that generates a tomosynthesis image from measurement projection data after substance extraction,
The substance extraction unit extracts the same equivalent substance of the projection data other than the projection angle using information on the extracted substance existing in the measurement projection data of the corresponding partial projection angle.
An X-ray tomosynthesis apparatus characterized by that.

  (2) In the X-ray tomosynthesis apparatus according to (1) above, the substance extraction unit includes a substance conversion unit that converts a pixel value of a region after substance extraction into a specific value without using a value of a peripheral region. Have.

  (3) In the X-ray tomosynthesis apparatus according to (2) described above, the substance extraction unit includes a substance conversion unit that converts the pixel values of the region after the substance extraction so as to compress the pixel value at a specific ratio.

  (4) In the X-ray tomosynthesis apparatus described in (3) above, the image generation unit performs a process of restoring on the tomosynthesis image the pixel value compressed by the substance extraction unit at a specific ratio. .

  (5) The X-ray tomosynthesis apparatus according to (4) described above, wherein the image generation unit includes an extraction image generation unit that generates an extraction substance image from a region extracted by the substance extraction unit. For the extracted substance region identified from the above, a process for restoring on the tomosynthesis image the amount of pixel values compressed by the substance extraction unit at a specific rate is performed.

  (6) The X-ray tomosynthesis apparatus according to (1) above, wherein the substance extraction unit is generated from an extraction image generation unit that generates an extraction substance image from a substance extracted region, and an extraction substance on the extraction substance image And an artifact detection unit that detects the artifact component, and performs a process of obtaining the difference of the artifact component from the tomosynthesis image.

  (7) In the X-ray tomosynthesis apparatus according to (5) and (6) described above, the substance extraction unit switches extraction processing according to imaging conditions, reconstruction conditions, subject, user settings, and the like.

  (8) In the X-ray tomosynthesis apparatus described in (7) above, the substance extraction unit uses the extracted substance information specified in the measurement projection data of the corresponding partial projection angle to calculate the corresponding projection angle. In addition to searching for the same substance extraction on the measurement projection data, it has a three-dimensional substance extraction unit for extracting the same substance for the measurement projection data other than the projection angle.

  (9) The X-ray tomosynthesis apparatus according to (8) above, wherein the substance extraction unit performs projection according to imaging conditions, reconstruction conditions, and the position (x, y, z) of the subject in the three-dimensional space. When the measurement projection data between the angles cannot be searched, a projection angle interpolation unit that interpolates the measurement projection data between the projection angles is provided.

  (10) The X-ray tomosynthesis apparatus according to (8) described above, wherein the substance extraction unit performs projection according to the imaging conditions, reconstruction conditions, and the position (x, y, z) of the subject in the three-dimensional space. When the measurement projection data between the angles cannot be searched, the substance is extracted based on the position information estimated from the measurement projection data of the front and rear projection angles.

(11) The X-ray tomosynthesis apparatus according to (10) above, wherein the substance extraction unit uses the pattern recognition of the subject to extract the substance based on the position information estimated from the measured projection data of the front and rear projection angles. Extract.
(12) The X-ray tomosynthesis apparatus according to (9) or (11) above, wherein the substance extracting unit measures and projects each projection angle after extracting the three-dimensional substance in addition to the three-dimensional substance extracting part. Perform a search on the data.
(13) The X-ray tomosynthesis apparatus according to (12) above, wherein the substance extraction unit uses an image processing technique such as a region expansion method, a graph cut, a level set, a snake method, and machine learning associated with edge extraction. Region extraction.

(14) In the X-ray tomosynthesis apparatus according to (13) described above, the substance extraction unit includes an extraction determination unit that determines pass / fail of the extraction result according to the set parameter value, and a parameter value according to the determination result A parameter changing unit for changing
(15) The X-ray tomosynthesis apparatus according to (14) above, wherein the substance extraction unit sets an allowable value for pass / fail judgment, and sequentially performs an optimization method such as a bisection method until the allowable value is reached. A parameter changing unit for changing parameters.
(16) In the X-ray tomosynthesis apparatus according to (15) above, the substance extraction unit determines an allowable value from the area or volume of the subject.
(17) The X-ray tomosynthesis apparatus according to (16) above, wherein the substance extraction unit has an excessive extraction when it is larger than an allowable value, an excessive extraction when it is smaller than an allowable value, or a projection angle in the front-rear direction. Pass / fail is determined using continuity based on the amount of substance extracted.

(18) In the X-ray tomosynthesis apparatus according to (17), the substance extraction unit includes a conversion measurement projection data unit that performs log conversion using measurement projection data and measurement projection data of air, and imaging conditions One of the measurement projection data and the converted measurement projection data is selected according to the reconstruction condition, the subject, the user setting, and the like.
(19) In the X-ray tomosynthesis apparatus according to (18) described above, the substance extraction unit includes a filter processing unit that performs filter processing for noise reduction in accordance with the selected measurement projection data.
(20) The X-ray tomosynthesis apparatus according to (19), wherein the image generation unit generates a tomosynthesis image from the measurement projection data, and calculates projection data and measurement projection data obtained from the tomosynthesis image by forward projection calculation. And a successive approximation reconstruction unit that sequentially corrects the tomosynthesis image so that.

(21) In the X-ray tomosynthesis apparatus according to (20) described above, the image generation unit converts the tomosynthesis image to a constant value when the pixel value is equal to or less than a predetermined value when sequentially correcting the tomosynthesis image.
(22) The X-ray tomosynthesis apparatus according to (21) above, wherein the image generation unit detects a specific value from the entire region or the local region in the pre-update image with the k-th sequential correction time as the pre-update image If the updated image after the (k + 1) th time is greater than or less than the specific value, a process for changing to the specific value is performed, and the specific value is changed for each update count.
(23) The X-ray tomosynthesis apparatus according to (22) described above, wherein the image generation unit specifies the minimum value of the entire region or the local region in the pre-update image with the k-th sequential correction time as the pre-update image When the image after the (k + 1) th update is less than or equal to the specific value, a process for changing to a specific value is provided, and the specific value is changed for each update count.

1 X-ray generator, 2 X-ray detector, 3 subject, 4 bed,
101 input unit, 102 photographing unit, 103 image generation unit, 103a data bus,
111 keyboard, 112 mouse, 113 memory, 114 central processing unit, 115 HDD device, 116 detector controller, 117 X-ray controller,
118 DAS, 119 memory, 120 central processing unit, 121 HDD device, 122 monitor,
131 imaging condition input unit, 132 imaging control unit, 133 imaging operation unit, 134 signal collection unit, 135 correction processing unit, 136 superabsorber processing unit, 137 image reconstruction unit, 138 image display unit,
141 imaging condition reception screen, 142 X-ray condition setting area, 143 reconstruction area setting area, 144 high absorber setting area, 145 imaging region setting area, 146 extraction method setting area, 147 measurement projection data screen, 148 pointer,
151 Three-dimensional substance search unit, 152 Two-dimensional substance search unit, 153 Extraction region conversion unit, 154 Three-dimensional data interpolation unit, 155 Three-dimensional pattern recognition unit, 156 Log conversion determination unit,
161 Three-dimensional differentiation processing unit 162 Three-dimensional boundary determination unit, 163 Three-dimensional region expansion unit, 164 Two-dimensional differentiation processing unit, 165 Two-dimensional boundary determination unit, 166 Two-dimensional region expansion unit, 167 Three-dimensional interpolation determination unit, 1683 Dimensional interpolation processing unit, 169 three-dimensional pattern recognition determination unit, 170 three-dimensional pattern recognition processing unit 181 Coronal plane, 182 Sagittal plane, 183 Axial plane, 184 measurement projection data with a projection angle of 0 degree, 185 in the projection angle direction in the X direction Section, section of projection angle direction in 186 Y direction,
191 n projection angle superabsorber region, 192 n + 1 projection angle superabsorber region,
201 three-dimensional substance search parameter optimization unit, 202 two-dimensional substance search parameter optimization unit,
231 Log conversion determination processing unit, 232 Log conversion processing unit,
301 Analytic reconstruction unit 302 Non-negative condition parameter storage unit 303 Forward projection processing unit 304 Difference processing unit 305 Back projection processing unit 306 Conditional image correction unit

For example, the superabsorbent body processing unit 136 has a more detailed configuration shown in FIG. 4A described later, but includes a three-dimensional material search unit 151. As shown in FIG. 4B, the three-dimensional material search unit 151 has a three-dimensional (x, y, z) in which two-dimensional (x, y) measurement projection data are arranged in the projection angle direction (θ = z). measurements projection data of you three-dimensional fine minute. Then, the three-dimensional substance search unit 151 determines, based on the differential value, whether adjacent data satisfies a predetermined condition with respect to the start point 41 set in advance in the measurement projection data of one projection angle. When the differential value satisfies a predetermined condition, the three-dimensional material search unit 151 sequentially expands the high absorber region in the direction of the adjacent data from the start point 41. The three-dimensional substance search unit 151 extracts a three-dimensional superabsorbent region by performing this process in the three-dimensional direction (region expansion method, see FIG. 4C). The three-dimensional material search unit 151 determines one or more points in the range (see FIG. 4D) that the extracted three-dimensional superabsorbent region occupies in the two-dimensional measurement projection data at other projection angles. The projection angle is set as the starting point in the two-dimensional measurement projection data.

Moreover, the superabsorbent body processing unit 136 may further include a two-dimensional substance search unit 152 shown in FIGS. 4D and 4E described later. 2-dimensional material searching unit 152, 2D fine-minute two-dimensional measurement projection data (FIG. 4 (d)). The two-dimensional substance search unit 152 determines whether adjacent data satisfies a predetermined condition with respect to the start point set by the three-dimensional substance search unit based on a two-dimensional differential value, and the differential value satisfies the predetermined condition In this case, the superabsorber region is extracted by expanding the superabsorber region in the direction of the adjacent data from the start point (region expansion method, FIG. 4 (e)).

In the three-dimensional differentiation processing unit 161, in step 171 of FIG. 5, two-dimensional measurement projection data arranged in the order of the detection element numbers in the horizontal direction x and the vertical direction y detected by the X-ray detection unit 2 is obtained for each acquired projection angle. For f (x, y, z) that is three-dimensional measurement projection data (three-dimensional sinogram) arranged in the projection angle direction θ = z, as shown in the following equation (2), for example, by a known image processing technique. A gradient image ▽ f (x, y, z) is calculated by performing partial differential calculation in a certain three-dimensional direction.

式（２）の▽ｆ（ｘ、ｙ、ｚ）は、ｆ（ｘ、ｙ、ｚ）の勾配を示す。ここで、第３項（ｕｚ）の前に係る係数αは、投影枚数（投影角度間隔）によって決まる係数であり、一般に投影角度間隔が大きいほど大きくなる。原点は、撮影開始後の１投影目における正面左上の検出器とする。ｕｘ、ｕｙは、横方向および縦方向における検出素子番号の単位ベクトルを示す。ｕｚは、投影角度方向の単位ベクトルを示す。式（２）は、３×３×３検出素子内の近傍６検出素子の値を用いて測定投影データの勾配画像を算出しているが、測定投影データのＳ／Ｎに応じて、例えばノイズが大きい場合は近傍１８検出素子の値を用いて勾配画像を算出してもよい。

In the equation (2), ▽ f (x, y, z) indicates the gradient of f (x, y, z). Here, the coefficient α related to the third term (uz) is a coefficient determined by the number of projections (projection angle interval), and generally increases as the projection angle interval increases. The origin is the detector at the upper left of the front in the first projection after the start of imaging. ux and ui indicate unit vectors of detection element numbers in the horizontal direction and the vertical direction. uz indicates a unit vector in the projection angle direction. Equation (2) is, 3 × 3 × 3 calculates the gradient image of the measured projection data by using a value near 6 test Demoto terminal of the detection element, but in accordance with the S / N of the measurement projection data, for example, if the noise is large it may calculate the gradient image with a value near 18 test Demoto child.

As a configuration different from that of FIG. 6 for realizing the first embodiment, the configuration of FIG. 7 will be described. In FIG. 6, only the conversion process to the specific value is performed, but in FIG. 7, the well-known log conversion process and image reconstruction are performed on the high-absorber projection data 406, and the high-absorber reconstructed image is obtained. 411 is acquired. At this time, the line-shaped artifact 413 generated from the high-absorber 412 is removed by a known threshold process or a feature extraction algorithm by using a property having different shapes or pixel values, and an image of the high-absorber 412 is obtained. Extract only. Next, for only the extracted region of the high absorber 412, the value of the high absorber 414 shown in the reconstructed image 409 is increased by multiplying, for example, the reciprocal of the coefficient d used for the conversion process to the specific value . Restore accuracy. At this time, it is not necessary to accurately obtain the pixel value of the superabsorbent body reconstructed image 411. If at least the region of the superabsorbent 412 can be extracted, the value of the superabsorber 414 can be restored by multiplying the inverse of the uniform coefficient d. Compared with the method of reconstructing the entire area by adding data by reducing the data size of the superabsorbent body reconstructed image 411 due to the effect of limiting the area, or by reducing the display byte by binarizing the pixel value, etc. Thus, a reduction in memory can be realized.

FIG. 8 shows a configuration further different from those in FIGS. 6 and 7 for realizing the first embodiment. In FIG. 8, the conversion processing of the specific value f ′ (x, y, z) is not performed, the reconstructed image 409 is reconstructed from the measurement projection data 405, and the difference from the above-described line-shaped artifact 413 is obtained. The line- shaped artifact 413 is removed and the corrected image 415 is acquired. Specifically, only the artifact 413 is extracted from the superabsorbent reconstructed image 411 by using a known threshold process, a feature extraction algorithm, or the like using a property having different shapes or pixel values. Next, by taking a difference from the reconstructed image 409 for only the extracted artifact 413, the value of the high absorber 416 shown in the corrected image 415 can be restored with high accuracy.

When the three-dimensional interpolation determination unit 167 determines that there is no connection, interpolation processing is performed using surrounding measurement projection data, and measurement projection data with connection virtually is created as shown in FIG. At this time, the interpolation process can use, for example, a well-known technique for generating an interpolation region using an average value of measured projection data of the same detection element at the front and rear projection angles.

Claims (15)

At least one of an X-ray generation unit that irradiates the subject with X-rays, an X-ray detection unit that detects the X-rays transmitted through the subject and obtains two-dimensional measurement projection data, an X-ray generation unit, and an X-ray detection unit An imaging unit having a mechanism unit for irradiating the subject with X-rays from a plurality of different projection angles, and X-rays included in the measurement projection data for each of the plurality of projection angles. A high-absorber processing unit that extracts each region of the high-absorber and converts the measurement projection data value of the region, and a tomosynthesis image based on the plurality of the measurement projection data processed by the high-absorber processing unit An image reconstruction unit for reconstructing
The high-absorber processing unit performs extraction of the region for the measurement projection data for each projection angle, using a start point set on the measurement projection data for each projection angle,
The high-absorber processing unit sets the start point in the measurement projection data at another projection angle based on the start point set in the measurement projection data at one projection angle. Tomosynthesis device. The X-ray tomosynthesis apparatus according to claim 1, wherein the superabsorbent processing unit includes a three-dimensional material search unit,
The three-dimensional material search unit calculates a three-dimensional gradient image by performing three-dimensional differentiation on the three-dimensional measurement projection data obtained by arranging the two-dimensional measurement projection data in the projection angle direction. Whether the adjacent data satisfies a predetermined condition with respect to the start point set in the measurement projection data is determined based on the value of the three-dimensional gradient image, and the value of the three-dimensional gradient image is determined according to a predetermined condition If the above condition is satisfied, a process of sequentially expanding the area from the start point in the direction of the adjacent data is performed in a three-dimensional direction to extract a three-dimensional area, and the extracted three-dimensional area is the other projection angle. One or more points within the range occupied by the two-dimensional measurement projection data are set as starting points in the two-dimensional measurement projection data at the projection angle. The X-ray tomosynthesis apparatus according to claim 2, wherein the superabsorbent processing unit further includes a two-dimensional substance search unit,
The two-dimensional material search unit performs two-dimensional differentiation on the two-dimensional measurement projection data to calculate a two-dimensional gradient image, and data adjacent to the start point set by the three-dimensional material search unit is predetermined. If the value of the two-dimensional gradient image satisfies a predetermined condition, the region is expanded from the start point to the direction of the adjacent data. The X-ray tomosynthesis apparatus is characterized in that a two-dimensional area is extracted as the superabsorber area.   2. The X-ray tomosynthesis apparatus according to claim 1, wherein the high-absorber processing unit measures the measurement projection data value in the region of the high-absorber when the X-ray absorption rate is lower than that of the high-absorber. An X-ray tomosynthesis apparatus further comprising an extraction region conversion unit that performs conversion processing into projection data values. The X-ray tomosynthesis apparatus according to claim 4,
The image reconstruction unit performs processing for restoring the measurement projection data value converted by the extraction region conversion unit to a pixel value corresponding to the measurement projection data value before the conversion processing on the tomosynthesis image. A featured X-ray tomosynthesis apparatus. The X-ray tomosynthesis apparatus according to claim 5,
The image reconstruction unit includes an extracted image generation unit that generates a high-absorber image from the extracted region of the high-absorber, and an artifact component generated by the high-absorber and the high-absorber from the high-absorber image. A high-absorber classification unit that classifies a region of the image and a region of the high-absorber after the separation on the tomosynthesis image is restored to a pixel value corresponding to the measurement projection data value. X-ray tomosynthesis device. The X-ray tomosynthesis apparatus according to claim 1,
The image reconstruction unit includes an extracted image generation unit that generates a high-absorber image from the extracted region of the high-absorber, and an artifact detection unit that detects an artifact component generated by the high-absorber from the high-absorber image An X-ray tomosynthesis apparatus, comprising: a difference between the artifact components from the tomosynthesis image. The X-ray tomosynthesis apparatus according to claim 1,
The high-absorber processing unit is interpolated when not connected to a determination unit that determines whether or not the region of the high-absorber at a certain projection angle is connected to the region of the high-absorber at an adjacent projection angle. An X-ray tomosynthesis apparatus comprising an interpolation processing unit that performs processing and virtually connects the processing units.   9. The X-ray tomosynthesis apparatus according to claim 8, wherein the determination unit is any one of the projection angle, a distance from the X-ray generation unit to the X-ray detection unit, a position and a size of the superabsorbent body. An X-ray tomosynthesis apparatus characterized by obtaining a region of a superabsorber in a projection angle direction based on one or more and geometrically estimating the presence or absence of connection of the regions at adjacent projection angles.   9. The X-ray tomosynthesis apparatus according to claim 8, wherein the determination unit is configured to determine the region of the adjacent projection angle based on the region of the high absorber for each projection angle extracted by the high absorber processing unit. The X-ray tomosynthesis apparatus characterized by determining the presence or absence of connection. The X-ray tomosynthesis apparatus according to claim 1,
When the superabsorber processing unit is not connected to the determination unit that determines whether the superabsorber region at a certain projection angle is connected to the superabsorber region at an adjacent projection angle, A three-dimensional pattern recognition processing unit that obtains the region of the superabsorber at the certain projection angle based on at least one of the shape and pixel value of the region of the superabsorber at another projection angle by the recognition process. A featured X-ray tomosynthesis apparatus.   The X-ray tomosynthesis apparatus according to claim 3, wherein the three-dimensional material search unit or the two-dimensional material search unit is configured such that the extracted three-dimensional region or the two-dimensional region is within an allowable range with respect to a reference value. If it is out of the allowable range, the value of the predetermined condition used when determining whether the differential value satisfies a predetermined condition is changed. An X-ray tomosynthesis apparatus comprising a parameter changing unit that performs   The X-ray tomosynthesis apparatus according to claim 1, wherein the high-absorber processing unit performs log conversion of the measurement projection data using the measurement projection data and the measurement projection data of air to generate converted measurement projection data. A conversion measurement projection data unit, and selects one of the measurement projection data or the conversion measurement projection data according to any of the imaging conditions, the reconstruction conditions, and the conditions set by the user; An X-ray tomosynthesis apparatus that extracts a region.   14. The X-ray tomosynthesis apparatus according to claim 13, wherein the superabsorber processing unit applies a noise reduction filter to the selected measurement projection data or the converted measurement projection data. Line tomosynthesis device. The X-ray tomosynthesis apparatus according to claim 1,
The image reconstruction unit generates a tomosynthesis image from the measurement projection data, the calculated projection data obtained from the tomosynthesis image by forward projection calculation and the measurement projection data are equal, and the pixel value is equal to or less than a predetermined value. A sequential approximation reconstruction unit that sequentially corrects the tomosynthesis image so as to convert it to a constant value without correcting the case,
An X-ray tomosynthesis apparatus characterized by that.

Images